The development of seats, in particular of vehicle seats, involves, among other things, the attaining of the greatest possible seat comfort because the occupants, under some circumstances, spend many hours relatively immobile on the seat. It is therefore desirable if vehicle seats provide the option for vehicle occupants to rest on them. What are known as “comfortable seats”, for example, provide this option. Seats of this type include a seat surface and a backrest which can be transferred from a sitting position into a resting position and vice versa. The sitting position is distinguished by an essentially vertical position of the backrest—for example, approximately 25° with respect to a perpendicular—and a correspondingly coordinated position of the seat surface, so that a vehicle occupant takes up an upright position. In contrast, in a resting position the backrest is inclined to a relatively pronounced extent, so that the occupant takes up a resting position similar to reclining.
In the case of an accident, there is the problem, in particular in the resting position, that a vehicle occupant is not restrained sufficiently despite having put on the seat belt. He/she may dive below the belt straps due to his/her position which is similar to reclining. This is called the “submarining effect”.
It is conventional to provide a three-point belt system for a normal vehicle seat with a plurality of belt tighteners, in order to increase the occupant's safety. For example, reference is made to German Published Patent Application No. 24 09 159, which describes a safety system for a motor vehicle seat, in which a three-point belt is tightened by three servomotors. The motors engage on the belt end fitting, on the belt buckle and on the belt-retracting mechanism and are activated in the case of an accident, as a result of which the belt strap is tightened. This tightening removes any belt slack which may be present and thus reduces the free play permitted by the seat belt, so that a vehicle occupant is restrained as immediately as possible.
An object of the present invention is to provide a safety device for a comfortable seat, which device may increase the safety of vehicle occupants.